Method of making rockfill foundations



p 1970. J. P. FRIEIN ET R 3,526,096

METHOD OF MAKING ROCKFILL FOUNDATIONS 7 Filed Dec. 11, 1968 3Sheetsfsheet 1 mvgmoas JOSEPH P. FREIN ARTHUR CASAGRANDE i BY v N I v. HATTORNEYS Sept. 1, 1970 FRElN ET AL I 3,526,096

METHOD OF MAKING ROCKFILL FOUNDATIONS Filed D60. 11, 1968 2 Sheets-Sheet3 INVENTORS JOSEPH P. FREIN ARTHUR CASAGRANDE ATTORNEYS United StatesPatent 3,526,096 METHOD OF MAKING ROCKFILL FOUNDATIONS Joseph P. Frein,Boise, Idaho, and Arthur Casagrande,

Belmont, Mass., assignors to Morrison-Knudsen Company, Inc., acorporation of Delaware Filed Dec. 11, 1968, Ser. No. 783,016 Int. Cl.E02d 27/04, 27/52 US. Cl. 6146 16 Claims ABSTRACT OF THE DISCLOSURERockfill foundation for support of a bridge pier, or the like, in whichthe lower portion of the foundation is made from large size, harddurable rock without any particular treatment. The upper portion of thefoundation is formed from individually compacted rock layers raising towithin a desired range of water surface. A surcharge of rockapproximately equal to the expected load is added to the compactedlayer. Surcharged rock is then used to form a breakwater around the workarea for construction of a weight distributor block on the upper surfaceof the compacted layers.

The present invention is concerned with rockfill foundations and theirconstruction methods.

In deep water work, for example at depths in excess of 300 feet, use ofthe air-floated caisson method for construction of bridge tower piers,and the like, presents insurmountable air pressure, caisson stability,and anchorage problems which, in the past, have precluded theoperational range of this method for over-water construction.

Conventional methods of dumping rockfill have not been able tosupplement the operational range of the airfloated caisson method orother known over-water con struction methods for deep water work. Inparticular, conventional methods of dumping rockfill do not eliminatethe possibility of sudden and substantial settlement or consolidationdue to earth tremors or under load. In waters subjected to tidalcurrents, and the like, it is not feasible to solidify rockfill withtreme concrete or grout, or to drill large diameter holes throughrockfill for addition of weight supporting concrete.

The present invention considerably extends the range of operations indeep and hazardous waters for bridge pier construction, and the like,while eliminating the possibility of foundation settlement orconsolidation under load or the likelihood of settlement under severeand prolonged earthquake vibrations.

These and other objects of the invention will be evident from adescription of specific uses of its teachings. The accompanying drawingswill be referred to for this description. In these drawings:

FIGS. 1 through 6 illustrate stages in forming a rockfill island for abridge tower, or the like, in accordance with the teachings of theinvention,

FIG. 7 is a cross-sectional view illustrating use of the invention forbent and cable anchorage foundation,

FIG. 8 is a cross-sectional view illustrating use of the invention forbent and cable anchorage foundation, and

FIG. 9 is a schematic cross-sectional view showing use of the inventionat various foundation locations in construction of a suspension bridge.

Prior to start of actual construction of a rockfill, boring logs ofsubsurface and subterranean profiles should be obtained in the generalarea of the rock foundation. These will determine depth and nature ofoverburden and the nature and placement of subterranean support.Preferably, the subterranean support should lend itself to establishinga substantially horizontal base within a practicable area of rockfill.If overburden is subject to compression, subsidence, or erosion, theoverburden should be excavated from the area of the lower foundttion.

Also, a source of hard, sound, durable rock capable of producing largestones with a minimum of fines should be established. Igneous rock,preferably granitic rock, is representative of satisfactory rockfillfoundation material for purposes of this invention.

Quarried rock, in relatively large stone sizes, is dumped inapproximately horizontal layers, without any particular treatment,covering the general embankment area. This lower foundation should bedumped to within a prescribed range of water surface depending on enduse of the foundation.

Individual horizontal layers of rock, of prescribed maximum depth, arelaid centrally of thefoundation, with each layer being individuallycompacted before addition of another layer forming a compacted zone witha substantially horizontal upper surface.

A surcharge of rock is added by stockpiling rock centrally on the uppersurface of the compacted zone. The surcharge of rock should beapproximately equal to or greater than the expected load for thefoundation. An ad vantage of this method, in addition to the safetyfactors involved, is that the foundation, if settlement or consolidationis tooccur, will occur as the surcharge is added so that practically notime lapse is required for settlement or consolidation. 7

The surcharge is then leveled or moved, with excess surcharge beingspread laterally over the side of the foundation to establish aplacement for constructing a Weight distribution block on the uppersurface of the compacted zone.

Referring, in sequence, to FIGS. 1 through 6 which illustrate use of theteachings of the invention in forming a rock island in deep water for abridge pier, and the like, a lower foundation 10 of large size stone islaid on subterranean support 12. The area of this foundation extendsover a predetermined outline on the subterranean support determined inpart by the outline of superstructure to be built on the foundation andangle of repose of the rock. Lower foundation 10 extends upwardly toapproximately feet below water surface in this embodiment.

FIG. 2 illustrates a subsurface vibrator 14 supported by barges 16 and18 compating individual layers 20 added to lower foundation 10. Theseindividual layers of rock do not ordinarily exceed 20-foot in depth andare compacted individually before the addition of other layers. Thedepth of individual layers to be compacted will be determined in part bythe vibration equipment available and the depth at which the first layercan be compacted will be determined in part by the effectiveness ofavailable vibration equipment at such depth. In the embodiment shown,five compacted layers are added to lower foundation 10 raising the rockisland to within approximately fifty feet of water surface.

As shown partially in dotted lines at 24 in FIG. 3, rock is stockpiledcentrally of the foundation to create a surcharge equal to or greaterthan the expected load for the foundation. In the embodiment shown, thissurcharge extends substantially above water surface. Upon completion ofthe stockpiling, the surcharge is leveled to within approximately 15feet above water surface. The surcharged rock is spread laterally asshown in FIG. 4, providing a broader 'base for excavation equipment.

As shown in FIG. 5, the centrally located portion of the surcharged rockpile is excavated and rock is placed outwardly of the excavation. Thisrock, in combination with the rock from leveling the surcharge formsdike 35 which acts as a breakwater for protection of the work area.Excavation extends downwardly to the upper surface of the compactedlayers and covers an area sufiiciently large for work equipment to builda weight distribution block and pier structure. In the embodiment shown,excavation extends to approximately 50 feet below Water surface.

A distribution block or bridge pier is built on the upper surface of thecompacted layers centrally of the foundation utilizing an open caissonor other means suitable for the shallow water conditions. Afterconstruction of pier 40, the lower edge of the pier, at the juncturebetween the pier and the compacted layer, is sealed with groutingcompound 44.

Breakwater 35 can be maintained in location or can be moved over theside establishing sidewall layer 48 as shown in FIG. 6. Sidewall layer48 adds to the sidewall strength of the foundation and removal ofbreakwater 355 permits navigation closer to pier 40.

The method described provides a presettlement and preconsolidation ofthe foundation. Spreading of the surcharge laterally achieves a widerisland than needed with side sloping at the angle of repose of the rock.This provides added protection for the foundation compensating for anytendency of the slopes to become flatter as a result of wave action andearthquakes. If wave action reduces the diameter, the minimum diametercan be maintained by armoring the upper portions of the slopes. At suchstage wave action should have established an underwater berm which wouldform a satisfactory base for founding armor stone.

The teachings of the invention are also applicable to establishingweight carrying rock embankments for shoreline construction as shown inFIGS. 7 and 8.

Referring to FIG. 7, lower foundation rock 50 extends from the shorelineout to an offshore position a sufiicient distance to provide lateralsupport and a horizontal area for compaction. Compacted zone 52 forcable anchorage 54 starts at the shoreline and extends offshore. Becauseof a leverage action of cable anchorage 54, a large portion of the loadis directed downwardly on compacted zone 52. During formation of thisfoundation, surcharge or rock equal to or greater than the load is addedto the compacted zone 54 and then moved laterally over the side of thecompacted zone.

Compacted zone 56 provides support for bent 58. Weight distributionblock 60 is cast on the upper surface of compacted zone 56 at about sealevel. Compacted zone 56 is also surcharged before building thedistribution block 60 and surcharge rock is moved laterally offshore towiden the embankment.

From the cross-sectional views of compacted zones 52 and 56 in FIG. 7,it will be seen that the area of compacted zone need not extend acrossthe full surface of a foundation. In practice the cross-sectional areasand depths of the compacted zones are determined in large part by theconfiguration of the structure to be supported and its load. Compactedzones 52 and 56 are formed from individually compacted layers and theweight distributor means are sealed at the upper surface of thecompacted zones as described earlier.

The height of compacted layers formed directly on subterranean supportis determined largely by topography with remaining portions of thefoundation providing lateral support. As shown in FIG. 8, compacted zone62 for bent 64 and compacted zones 66 and 68 for cable anchorage 70 arecompacted directly on subterranean support 72. Portions 74 and 76 of therock foundation are laid without any particular treatment and providelateral support and protection against wave action. Surcharging ofcompacted zones is applied as described earlier with surplus stone beingused to widen the foundation.

FIG. 9 shows the profiles or rock foundations formed in accordance withthe present invention. Rock islands 80 and 82 support bridge towers 84and 86 respectively. Rock foundation 88 supports cable anchorage 90 andbent 92. Rock formation 94 supports cable anchorage 96 and bent 98.

Various modifications in the specific embodiments described will beavailable to those skilled in the art in the light of this disclosuretherefore, the scope of the present invention is to be determined fromthe appended claims.

What is claimed is:

1. Method for constructing a rockfill island for support of a bridgetower, or the like, comprising the steps of:

dumping hard durable rock in approximately horizontal layers over apredetermined lower foundation area and extending upwardly to Within apredetermined distance of water surface,

establishing a zone of compaction having an upper surface and ofpredetermined height and cross-sectional area by compacting a pluralityof individual, limited-height substantially horizontal rock layers, witheach individual rock layer being compacted before adding an additionallayer,

dumping a surcharge of rock on the upper surface of the compacted zone,such surcharge of rock adding a weight to the foundation approximatelyequal to or greater than expected load to be carried by the foundation,and

removing at least a portion of the surcharged rock to establish aplacement for weight distributor means on the upper surface of thecompacted zone.

2. The method of claim 1 in which the compacted layers of rock are addedto the lower foundation of hard durable rock raising the overall heightof the foundation.

3. The method of claim 1 in which surcharged rock is removed byexcavating centrally of the foundation to the upper surface of thecompacted zone.

4. The method of claim 1 including the following steps carried out priorto dumping the hard durable rock over the predetermined lower foundationarea,

making subsurface borings to determine subterranean support profile, and

excavating undesirable overburden from the foundation area.

5. The method of claim 3 in which the surcharge of rocks extends abovewater surface including a step prior to excavating centrally of thesugrcharge of:

leveling surcharge to within a prescribed distance of water surface withsurplus surcharge being moved laterally.

6. The method of claim 3 including the step of:

placing excavate-d rocks contiguous to the excavation to form a rockdike which acts as a breakwater surrounding the excavation.

7. The method of claim 3 in which the excavation step is carried outthrough at least a portion of the surcharge rock to the upper surface ofthe compacted layers.

8. The method of claim 1 including the step of:

casting weight distributor means on the upper surface of the compactedlayer.

9. The method of claim 8 in which the periphery of the weightdistributor means at the upper surface of the compacted zone is sealedwith a grouting compound.

10. The method of claim 6 in which the breakwater dike about theexcavation area is removed to a predetermined depth below water surfacebut not below the upper surface of the compacted zone, such breakwaterrock being moved laterally over the side of the foundation to increasethe lateral area at the foundation in the horizontal plane of the uppersurface of the compacted zone.

11. The method of claim 1 in which the lower foundation of hard durablerock is dumped to a height approximately feet below water surface.

12. The method of claim 11 in which a plurality of rock layers ofapproximately 20-foot depth each are compacted on the lower hard durablerock foundation with the height of the compacted layers extending to aheight approximately 50 feet below water surface.

13. The method of claim 3 in which the centrally located excavationthrough surcharge rock extends approximately 50 feet below watersurface.

14. Method of constructing a rockfill embankment for founding footingsfor bridge piers, bents, anchorages, and the like, comprising the stepsof dumping hard durable rock over a predetermined lower foundation area,

establishing a zone of compaction having an upper surface andpredetermined height and cross-sectional area by compacting a pluralityof individual, limitedheight, substantially horizontal rock layers, witheach individual rock layer being compacted before adding an additionalrock layer,

dumping a surcharge of rock on the upper surface of the compacted zone,such surcharge of rock adding a load to the foundation approximatelyequal to or greater than the load to be carried by the foundation, and

removing at least a portion of the surcharged rock to establish aplacement for weight distributor means on the upper surface of thecompacted zone.

15. Method of claim 1 in which peripheral portions of the weightdistributor means at the upper surface of the compacted zone are sealedwith a grouting compound.

16. The method of claim 1 in which the rock embankment extends offshorefrom a shoreline with the compacted zone extending from subterraneansupport to water surface and the remainder of the dumped level rockproviding lateral support for the compacted zone.

References Cited UNITED STATES PATENTS 1,489,428 4/1924 Cushing 6l42,382,763 8/1945 Young 6146 2,939,290 6/1960 Crake 6146.5

JACOB SHAPI'RO, Primary Examiner US. Cl. X.R. 61--4, 50, 52

